Every reform begins and ends with those who implement it on a daily basis. Educational reform begins in the classroom with a specific teacher and a specific class, that is with each individual student. It is up to the teacher to choose between the options that are offered to him, but also between those that are not offered to him, but he can find them by himself. Official reform documents can be confusing for teachers, seem vague and imprecise, or even flawed, but they offer the teacher the freedom to make decisions and be the bearer of reform. Both in science and teaching, and among PhET simulations for mathematics and physics, there is a certain difference in approach. PhET simulations for physics offer more options and to some extent correspond better to learning outcomes than simulations for mathematics. The possible difference is due to the complexity of the concepts that are in the center of the study of individual simulations, the diversity of curriculum documents, the extensiveness of the teaching material or due to differences in the sciences of mathematics and physics. PhET simulations can enrich the teaching process and increase the student's interest in inquiry-based learning. They can help the teacher in those topics that are covered by the learning outcomes prescribed by the curriculum or can be used in other forms of teaching and extracurricular activities.