How was Cassie rescued from Mr Sims in roll of thunder hear my cry?

Cassie was rescued from Mr. Sims in roll of thunder hear my cry because when Cassie bunmped into Lillian Jean, she had to applologize to Lillian Jean for "pushing" her. Big Ma made Cassie appologize to the Sims. For a moment, Cassie understood why Big Ma made her applologize (so there would not be any fighting going on between a black girl and a white girl).