Test Tutor is a great skill-building resource. The landing page will show that the site features assessments for Grades 1-6. Grade One has just four skill levels, while the rest typically have twelve or more.
Each skill level focuses upon a specific reading skill (author's purpose, cause and effect, summarizing, sequencing, etc.). The level begins with a description of that skill and why it's important. Students then read a passage and answer multiple choice questions. I like using this site because both incorrect and correct answers provide students feedback