This research has been carried out with the aim to discover whether students gain better learning results when a concrete teaching unit is presented by using a traditional (frontal) teaching method and expository teaching, or by using inquiry-based learning, as well as whether inquiry-based learning helps obtaining a long-term memory of the acquired knowledge of concrete teaching units. In this research, we have also assessed the students’ readiness for inquiry-based learning, considering curriculum and the common teaching and learning methods. The research was carried out during school years 2016/2017 and 2017/2018, and comprised 76 students of second grades of Ruđer Bošković technical school and natural sciences program grammar school in Osijek. It consisted of presenting teaching lessons “Monocotyledons” and “Dicotyledons”, determining learning habits of each student by polling, establishing the most common manner of teaching by polling and of the initial, final and repeated final test. In one grade of grammar school, teaching units were presented by using frontal teaching method and expository teaching, while in two grades, one also at grammar school, and one in technical school for obtaining vocation: ecology technician, the units were presented by using inquiry-based learning. We have established that the students at grammar school which used inquiry-based learning are more successful than those students of the same program which were taught by using traditional (frontal) method and oral presentation method, and also more successfully than students - ecology technicians with whom the inquiry-based learning was also used. Students of grammar school and students - ecology technicians which used inquiry-based learning gained better results at final and repeated final test in comparison with the initial test. By reviewing written tests and analyzing polls on common manners of teaching and learning, we have assessed that the students of grammar program are better prepared for inquiry-based learning than the students - ecology technicians.