“Ma” (** out of four) was a pretty routine thriller about a group of high-schoolers (Diane Silvers, McKaley Miller, Corey Fogelmanis, and others) who befriend a lonely older woman (Octavia Spencer) who lets them party in her basement but they soon realize she’s a real sicko and that their lives are all in danger. Spencer is good as usual but film treads on all-too-familiar territory to provide many scares or thrills. Disappointing reteaming of her and director Tate Taylor who previously scored big with “The Help.”