Ugh. First thing - if you have reading teachers at school, hit them up.
Next: Are you specifically teaching main idea/inferences? I find the Jamestown Readers extremely helpful for practice. They can practice text marking, and the questions provide practice for them.
For main idea, have them search for repeated words/phrases/ideas. Text mark.
For inferences... are they making they're own inferences or deciding if an inference is correct or faulty? If they are choosing, have them look for what I call "extreme words" - EVERYone, NObody, ALL people, etc. If it the statement claims an extreme, then it is not a correct inference.
Hope this helps some...