Another possibility is that your son does not want to be in the magnet school. Is the pressure too much? How are his relationships with other students? Does he want out? What does he say? Very few seventh-graders are really ready emotionally and mentally for highly structured intellectual studies, even if they are very bright. Right now your son is not benefiting from this educational structure, as is shown by his grades and his deceptions. He may benefit more by being in the regular school with less pressure and time to mature. With time in the regular school, he may realize that he wants more of a challenge and be willing to do the work necessary at the magnet school.
Whatever your decision, make it together as a family after exploring all the aspects of the problem.