Why did Stacey disobey mama and go to the Wallace Store?

Stacey has taken the fall for T.J's cheating. After school T.J runs away. Stacey is angry. He and the other kids run after T.J. Moe Turner tells them that T.J. went to the Wallace Store. This is why Stacey follows.

Stacy was told that his brother T.J. was in the store