Of course, I can't ask that question about another teacher without also asking myself the same thing. Simply because my students are occupied and rarely wasting a minute does not mean they are engaged in what they're doing. They could just be going through the motions, and if that's the case, I'm wasting their time.
I believe engagement happens when students find purpose and meaning in tasks. If the work is authentic and founded on the interests of their own world, they are more likely to put their hearts into it. Engagement is also more likely to occur when tasks are not too easy or too hard. Both extremes are off-putting and difficult to embrace.
At a glance, I might easily assume that my students are engaged, when it's possible, if I look more deeply at what they're doing, they might just be on-task. Day after day and lesson after lesson, I want to consistently challenge myself to dissect what I'm asking of my students. Will this engage them or will it keep them on-task? The latter just isn't good enough.