Hypothesis generation is an important but difficult process for students. This study investigated the effects of providing students with support for hypothesis generation, with regard to the testability and complexity of the generated hypotheses, the quality of the subsequent inquiry learning processes and knowledge acquisition. Fifty-two secondary school students completed three prior knowledge tests and worked on an inquiry task in the domain of force and motion, concerning the topic of Newton's first law of motion. They received either a set of terms (variables, conditions and relations) to help them generate hypotheses (T condition, n = 23) or the same set of terms plus a partial hypothesis to start from (T + PHy condition, n = 29). Results showed that students in the T + PHy condition generated more complex hypotheses, performed better at data collection and acquired more domain knowledge than students in the T condition. No effects of prior knowledge were found.