A: This is a dispute between the Rishonim. The Rambam wrote in his commentary on the Mishnah (Shabbat chap. 23 and quote in the Beit Yosef Orach Chaim 307) that it is forbidden to read books of wisdom, which are not Torah, on Shabbat and Yom Tov. This is interesting since the Rambam is usually thought to be the authorities most open to general wisdom. But according to the Ramban (Beit Yosef ibid.), it is permissible to read medical books since they contain wisdom. These two opinions at quoted in the Shulchan Aruch (ibid. #17): "It is forbidden to study on Shabbat and Yom Tov aside from words of Torah, and even books of wisdom are forbidden, and there is an opinion which permits it." The Mishnah Berurah (380:65) indicated that we act leniently but it is proper to be strict. The basic halachah is therefore that it is permissible to learn secular subjects on Shabbat but it is certainly proper to be strict. If one follows the permissible view, it includes school reading or studying for a test on the condition that one enjoys it. If such activities cause stress and fear over a test, one should refrain from studying.
It is related that the Rama once quoted a thought from Aristotle in one of his Teshuvot, and the Meharshal was upset that instead of learning Torah he learned Aristotle. The Rama responded that he was free from transgression, and even though he brought a quote from Aristotle, heaven and earth can testify that he did not learn any of his books. On Shabbat, when others were taking walks, he would learn Moreh Nevuchim and books about nature, and he saw the thought from Aristotle there. During the week, he only learned Gemara and Halachah (Shut Ha-Rama #7). We therefore see that instead of taking a stroll on Shabbat afternoon, the Rama strolled in books about nature.