Do they even know what a constructive response question is or how to answer is? I think this should be modeled over and over just like any other skill we teach. Sometime students see or hear the word test and they run for the hills and that is just a normal student. My daughter has an IEP and when she hears a test is coming she tries to stay home sick. We have her teachers email us when a big test is coming just so we know ahead of time so she goes to school. Tests are scary and long answers and even worse, they hate them and in some ways I do not blame them for skipping them, but we have to teach them that those questions are important and they can be answered if they take their time and read through them one at a time and answer them the best way they know how and with our help preparing them they can do this.

Students may benefit from teacher modeling and exemplars to teach students the purposes and expectations for constructed response items.

In addition to modeling and practicing constructed response questions with students, one strategy that I have found useful is to show students sample answers to these types of questions. Sample student responses give the class a chance to critique the work of others and practice justifying their responses before having to do it on a test.

I have witnessed this myself. I start the beginning of the year off with sentence frames that help these students have a frame of reference or a starting point for setting up a constructed response question. This really helps because they are able to get a starting point and then use their knowledge to complete the sentence.

Teach students how to break down the questions to get them more comfortable with what the question is asking. Also teach them a strategy for answering them, such as R.A.C.E. Restate the question, Answer the question, Cite evidence, Explain the evidence. Model this strategy for them. It will take time to get a perfect answer, but you will start getting more than "IDK" or them leaving it blank.