This research aimed to assess the knowledge of photosynthesis among students in agricultural education and understand the influence of the contextual factors on it. In photosynthesis, biomass is produced, so understanding these processes is essential for successful agriculture. The research sample consisted of 330 students in agricultural education in Slovenia. Data were collected with a knowledge test and a contextual questionnaire. Better knowledge of photosynthesis was positively related with higher awareness of the importance of biology as a science and of photosynthesis. There was no significant relation between the knowledge of photosynthesis and positive attitudes toward biology lessons. The average achievement on the knowledge test of photosynthesis was 56%: the highest on the item about energy and the lowest on the item about the primary purpose of photosynthesis. Between these two achievements was the knowledge of reactants and products in photosynthesis, and the knowledge concerning chlorophyll. Considering these results, improvements should be made in teaching. For this population, more experimental and less theory-based lessons were suggested. The findings could benefit biology and science teachers in agricultural education and help improve national curriculum for biology in agricultural programmes.