Due to the overall development in education brought about by democracy Portugal faced a huge development in Higher Education (HE) since the beginning of the 1980’s until 2003. Then the trend began to reverse due to demographic evolution (OECD 2006). However, the net graduation rate for Portugal compares badly with most EU member states (32,3%  against 34,9% and 36,4% for EU-19 and OECD averages, respectively, in 2005). Besides, survival rates in HE are relatively low when compared to other EU countries: 66% against 75% for Spain (2005) [1].  

This means that the Portuguese production function of HE faces considerable deadweight losses, under the form either of retention rates or of quitting flows. (Un)success in academic performance at HE 1^st cycle becomes more important now that Bologna Chart is on the way for tertiary education. As a matter of fact institutional arrangements became more strict under Bologna, namely throughout shorter time duration for 1^st. cycle completion (from 4 to 3 years,  in most Portuguese social sciences graduation programmes) though syllabuses’ extension and complexity remained almost the same.

It seems therefore most pertinent to investigate the main factors affecting students’ performance at the beginning of higher education.

 Given the syllabuses interdependency between sequential graduation years for most subjects it looks advisable to analyse a bundle of 1^st. year core disciplines and investigate the main features behind the corresponding (un)success rates.  Actually those disciplines will provide the main qualifications upon which further developments will settle along the graduation programme.

Most research carried on higher education success and failure rates still relies upon cross section methodologies supported by synchronic data. But learning is by itself a rather complex multidimensional and time dependent process, mainly when it coincides with transitions to adult life (Bidart & Lavenu, 2005).

Therefore the main purpose of this paper consists in systematically assess semi-longitudinal data on individual trajectories retrieved from ISEG Pedagogic Observatory in order to approach the main determinants of success\failure at the beginning of 1^st cycle as a dynamic and past dependent process. We set the number of enrolments   needed to successfully complete two 1^st year\1^st semester disciplines, common to the four graduation programmes, as a proxy for (un)success. 

Our main hypotheses are therefore:

- relative success in completing core 1^st year graduation subjects, will be negatively affected by lower SES of the family of origin, poor performance during previous schooling and H.E. trajectories, participation in the labour market;

- gender outcomes will most probably differ either relatively to success rates or to patterns of enrolment induced by the above determinants.

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