In recent years, empirical studies have investigated factors influencing the effectiveness of teacher professional development programs. These studies have stressed empirical evidence regarding the influence of the quality and quantity of learning opportunities on the effectiveness of teacher professional development programs (Borko, 2004). But additionally, the person of the facilitator itself is also believed to influence the effectiveness of teacher professional development programs – although the facilitator has been less in the focus of empirical studies so far (Bell et al., 2010; Borko, 2004; Carney et al., 2019; Linder et al., 2013; Lipowsky & Rzejak, 2015). In this context, it is assumed that specific characteristics of the facilitator – e. g. knowledge, beliefs, enthusiasm (Lipowsky & Rzejak, 2015) – have an impact on the effects of teacher professional development programs and influence the extent to which the facilitators succeed in promoting the teachers’ knowledge addressed in the professional development program. In a professional development program in the field of early mathematics education this would relate mainly to mathematical pedagogical content knowledge, as mathematical pedagogical content knowledge is understood as a prerequisite to analyze children's mathematical development and to adaptively support it in (unplanned) everyday learning situations (Gasteiger & Benz, 2018). Next to the extent to which the specific characteristics of the facilitators have an impact on promoting teacher’s knowledge, they may also be responsible for the extent to which facilitators succeed in promoting teachers' enjoyment of the content of the professional development program (Lipowsky & Rzejak, 2015) and thus motivate teachers to transfer the knowledge they have acquired into their daily work (Richardson, 1996). Due to a lack of empirical studies, the exact characteristics that distinguish successful facilitators from less successful facilitators are hardly clear at the moment (Lipowsky & Rzejak, 2015).

Early childhood teachers – the targeted participants of the professional development program addressed in this study – expect facilitators to have own teaching experience as an early childhood teacher (Linder, 2011; Linder et al., 2013). However, there is a lack of empirical evidence on the extent to which a facilitator’s teaching experience as an early childhood teacher actually determines the success of a professional development program. This desideratum will be addressed in the following. Specifically, we will look at (1) the extent to which the teaching experience of facilitators influences the development of early childhood teachers’ mathematical pedagogical content knowledge in the context of a teacher professional development program. Since it is especially true for early childhood teachers that enjoyment of mathematics is an important predictor for the implementation of mathematical pedagogical content knowledge in daily work (Anders & Rossbach, 2015; Blömeke et al., 2017), we also investigate (2) to what extent the facilitators succeed in promoting early childhood teachers' enjoyment of mathematics based on their own teaching experience.

In summary, the following research questions emerge:

RQ 1: To what extent does the teaching experience of facilitators affect the development of mathematical pedagogical content knowledge (MPCK) of early childhood teachers in the context of a teacher professional development program?

RQ 2: To what extent does the teaching experience of facilitators affect the promotion of early childhood teachers' enjoyment of mathematics in the context of a teacher professional development program?

As part of a quasi-experimental intervention study, 83 early childhood teachers (76 female, 7 male) participated in a teacher professional development program on designing learning environments to support early mathematics education processes in early childhood settings. The professional development program was carried out by 8 facilitators. While 6 of the 8 facilitators had between 11 and 30 years of teaching experience as early childhood teacher, the other two facilitators had no teaching experience as an early childhood teacher. The professional development program was evaluated by measuring early childhood teachers’ MPCK and enjoyment at two points of measurement before and after their participation in the professional development program. The MPCK of early childhood teachers was assessed using a standardized test instrument that has been developed by Blömeke et al. (2015). The test instrument includes a total of 35 items (30 multiple-choice-items; 5 open-ended-items) which assess MPCK concerning the development and diagnosis of mathematical skills of children aged three to six years as well as the playful design of mathematical learning environments with the aim of promoting mathematical skills (Blömeke et al., 2015). The 35 items were coded dichotomously (0 = not correct; 1 = correct) and Rasch-scaled (EAP reliability = 0.58). The z-standardized WLEs were adopted as the performance scores of the early childhood teachers. The early childhood teachers' enjoyment of mathematics was assessed in a questionnaire using five-level Likert items (ranging from 1 = "I strongly disagree" to 5 = "I strongly agree"), which were also developed by Blömeke et al. (2015). The reliability of the enjoyment scale is Cronbach's α = .82. A t-test for dependent samples was used to analyze whether the early childhood teachers who participated in the professional development program were able to increase their MPCK and their enjoyment of mathematics from measurement time point 1 to 2. Based on these findings, analyses of variance with repeated measures were used to examine the extent to which differences in the development of the early childhood educators' MPCK and enjoyment of mathematics can be explained by the teaching experience of the facilitators. The categorial variable “teaching experience” divides the early childhood teachers into two groups. One group consists of those early childhood teachers (n = 64) whose facilitators have at least 11 years of teaching experience. The other group comprises those early childhood teachers (n = 18) whose facilitators have no teaching experience as early childhood teacher.

With respect to research question 1, it can be concluded that the facilitators succeeded in promoting early childhood teachers’ MPCK (t(81)=-2.23, p<.05, d=0.27). Based on analysis of variance with repeated measure, however, neither an influence of facilitators teaching experience (F(1, 80)=2.18, p=.14) nor an interaction effect of measurement point and teaching experience (F(1, 80)=0.06, p=.81) was found for early childhood teachers’ MPCK. In addition to promoting early childhood teachers’ MPCK, the facilitators also succeeded in promoting early childhood teachers' enjoyment of mathematics (t(81)=-6.28, p<.001, d=0.78) (RQ 2). An analysis of variance with repeated measures for early childhood teachers' enjoyment of mathematics revealed an interaction effect of measurement point (F(1, 80)=13.77, p<.001) as well as an interaction effect of measurement point and teaching experience of the facilitators (F(1,80) = 9.97, p<.01). Based on these results, the facilitators with teaching experience are not more successful in promoting early childhood teachers’ MPCK than those facilitators with no teaching experience. However, the facilitators with teaching experience were more successful in promoting early childhood teachers' enjoyment of mathematics than those facilitators without teaching experience. Considering the importance of early childhood teachers' enjoyment of mathematics for implementing learning opportunities supporting children’s mathematical development (Anders & Rossbach, 2015; Blömeke et al., 2017), teaching experience as early childhood teacher seems to be a relevant characteristics of facilitator working with early childhood teachers. However, e. g. caused by relatively small amount of early childhood teachers taking part in the study additional empirical research is necessary to confirm validity of given results.

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