Jeff Lacy was tutored by Eric in I Never Sang for my Legal Guardian because he was failing and he needed a C average to get one of the many athletic scholarships offered to him. Eric tutored him because Mr. Feeny hoped that the tutoring would help Eric's grades as well.
Part of Jeff's stupidity was his inability to focus. While studying with Eric at Chubbie's, Anita asked him if he wanted to go driving around, and he immediately said yes and left. He's also just plain dumb, saying "Louie the King" followed "Louie XIV".
According to Eric, he actually can burp through his ears.