Reading Comprehension Conundrum

I continue to experience the same problem with each reading assessment that I assign, and I am wondering if anyone else experiences it as well and/or has input and suggestions. When I administer a reading assessment, I make absolutely certain that it is comprehensible to my students. If there are any words that my students haven't learned and shouldn't be able to figure out with a few squints of concentration, I footnote it. The point is to assess whether or not they understand the structures that they are supposed to have acquired when read in context. So I get really frustrated when I grade an assessment and the scores average a Developing (C) or--worse--an Emerging (D)! Occasionally, I can look back and see that I was trying to stretch them a bit too much. This was the case with my Spanish A kiddos last week. But those instances are few and far between because I am SO CAREFUL when designing reading assessments. The problem, I have discovered, is that my students are really, really, really bad at answering questions. I have discovered this pattern because I will often give papers back to students and have them write out the translations of the readings, and they translate the entire thing without significant errors. Then, I ask them to go back and re-answer the questions. Most of the time, they say, "OH DUH!" and correct their mistakes. Oftentimes, however, they still don't get it. About a month ago, this sentence appeared in a reading for Ladrones: "The robbers robbed the same store four times". The question was, "How many different stores were robbed?" The answer, obviously, was ONE. Even after students translated the sentence, however, many were unable to answer the question. Do you think that my questions are just too hard?? Is this nothing more than a result of my students' low ENGLISH reading comprehension? Is it fair and accurate to accept a correct translation of the reading as proof of their Spanish reading comprehension, or is the fact that they can't answer questions (in English) about a Spanish reading proof that their Spanish reading comprehension is low? I need input, people!!!!!!!  Help!!