Mishnah Berurah 155:3 says:
חייב אדם ללמוד בכל יום תורה שבכתב שהוא תנ"ך ומשנה וגמרא ופוסקים, a person is obligated to learn every day [the] Written Torah, which includes TaNaCH - Torah, Prophets and Writings - and Mishnah, and Gemara and work of Halacha.
I went to a Jewish Orthodox elementary and high school. They were primarily dedicated to learning Gemara. Why aren't Jewish elementary and high schools dividing up their day learning TaNaCH, Mishnah, Gemara, and works of Halacha, as the Mishnah Berurah recommends?