The National Reading Panel concludes that making inferences is central to reading comprehension. When readers make inferences they interpret ideas not stated explicitly in the text and draw appropriate conclusions. They go beyond what the author has written on the page. Readers put together clues from the text and make evidence-based guesses about character motives, the plot, the problem, the solution, etc.
Websites on Making Inferences:
Online Inference Test
Math Literacy: Making Inferences
Active Notes for Making Inferences - PDF