How are you adjusting reinforcement to reduce maladaptive behavior? Can you reinforce a more appropriate, alternative behavior to replace the maladaptive behavior?
Stop answering the questions and reinforce an alternative behavior! If the student is asking the same question over and over again and you are answering each time, you are reinforcing the behavior. Instead, re-direct him. You could re-direct him to a visual reminder cue, a task or activity, or his coping plan, for example.
In some cases, it may be appropriate to institute a rule (explained verbally and depicted visually) that indicates that the student may ask his question once and he will get his question answered once (by one person in the room), and then no one else will answer that question again.
In the initial stage, when you stop responding to these perseverative questions at the same rate as you did previously, you should expect that the behavior will get worse, before it gets better. This behavior used to be reinforced, and now it is not (or it is reinforced at a lower rate). The student will try even harder to get your attention and to obtain a response, because he is accustomed to getting these questions answered. It is critical that everyone (instructors, family members, and peers, to the degree possible) respond in a consistent manner. Some instructors may continue to reinforce the behavior by verbally responding to every question while other instructors work to reduce the behavior and increase an alternative behavior (i.e. differential reinforcement). This inconsistency can actually lead to increased attempts by the student to engage in perseverative questioning.
Again, find a behavior to reinforce in the place of the perseverative questioning.
What are some reinforcing consequences you can deliver either immediately following the desired replacement behavior, or following a period where the student would have been inclined to perseveratively question, and did not?
Are you using labeling and social praise to make the contingency between desired behavior and reinforcing consequence clear to the student?
What reinforcing consequences can you arrange that are more naturally or intrinsically connected to this targeted behavior?