Why does frederick call mr. auld’s forbidding his learning how to read “invaluable instruction? ”

Because he unwittingly gives him the key to mental freedom, at a moment Frederick states "if you teach that black person (speaking of myself) how to read, there would be no keeping him. It would forever unfit him to be a slave." Once he knew the world that Mrs. Auld taught him, it was imposible for him to be satisfied being a slave.

an interest group is an organization whose members share common concerns, and try to influence government policies that impact those concerns. elected officials frequently complain about the influence of "special interests" on american politics.