The relationship between needs fulfilment and the professional development of student teachers.In immediate on the spot teaching behavior, student teachers fall back on unconscious action tendencies and behaviors, which are often ineffective and which student teachers during reflection when looking back afterwards find undesirable. Such unconscious action tendencies are triggered by needs, especially the needs for autonomy, for competence and for relatedness (Ryan & Deci). Needs are important to feelings of well-being and satisfaction, intrinsic motivation and functioning in general. By equifinality, needs activate unconscious processes such as auto-motives, unintended thoughts (Bargh), Gestalts, action tendencies, thoughts and beliefs. Needs that are thwarted reduce successful functioning, slow down professional development, activate defensive mechanisms, can lead to compensatory motivation and rigid behavior. The activation of core strengths such as trust, engagement, willpower, creativity (Seligman) can help student teachers towards a positive change in their development. The focus of this research is the relationship between needs fulfilment and the professional development of student teachers. We will report on relations between needs fulfilment, satisfaction, functioning and development of student teachers.