Students are generally required to demonstrate diverse skills when writing their bachelor thesis. Accordingly, examiners are expected to consider all these skills when assessing the thesis, regularly with one overall grade. In this study, we examine which criteria of a rubric contribute most to the overall assessment. The study is performed through quantitative analyses of 318 theses of undergraduate biology students. The analyses demonstrate that all criteria scores are predictive, but that "scientific quality" and "professional attitude" give the best prediction of thesis grade, together with "structure." The predictiveness of "scientific quality" and "professional attitude" correspond with the instructions given to examiners that these are important criteria to consider. Presentation-related criteria scores on "writing skills" and "expressing catchy and justifying titles" give the lowest prediction of grade. This study identifies that some criteria appear more predictive for low grades than for high grades, with "professional attitude" being a good predictor for low grades and "abstract" being a good predictor for high grades. We recommend similar analyses for students to help them prioritise the most relevant criteria, for supervisors to instruct students on these criteria, and for education managers to evaluate whether bachelor theses are assessed on the criteria they find most relevant.