Well, one way to look at is this: you can only do what you can do. You need help. You are only one person. Thankfully, you have a rich source of differentiation help you may not be tapping into, your students. If we assume that one of the most important elements of differentiated instruction is to create activities that are relevant to the students at their current ability level, then who better to assess that level than the kids themselves? This may sound a little far-fetched, but let me explain with an example from my classroom.
My students are always working in groups. They sit in groups, plan collaboratively, and negotiate roles on a daily basis. They know each other very, very well. Thankfully, there is a true culture of kindness in the room and the kids really take care of each other. When explorations are underway, I no longer have to worry about whether a particular activity is meeting the current level of achievement of my students because they have a constant stream of meaningful feedback from their own group members. I would never be able to provide as many and varied comments about what looks good, how to approach the job in an easily understood way, how to understand the task at hand or simply ask the simple question, 'Are you getting it?" When the students work in teams, they pull together, helping each other along at a level that makes sense to them. There's true differentiation.
Where do I step in? Usually, one of the students will quietly let me know one of their team members is struggling. I love this, because inquiry based learning has freed me up to go and spend meaningful amounts of time with kids to truly address their needs. The rest of the class is so caught up in their work, they hardly ever miss me. I can delve into the learning styles and interests of my students because I have the time for individual assessment in the course of any given day. Because exploration work is done over the course of days or weeks, nothing is so time-sensitive that I can't take the time to deal with a struggling student and provide true support.