For math you can do flex grouping, also based somewhat on ability as determined through pre-tests and personalties, and this too is totally permissible. It allows for smaller groups and different pacing of curriculum, as well as remediation and enrichment.
Yet, if you take away the gentler names and introduce the word “tracking”, then both of these scenarios lose their luster. So I wonder, out loud as usual, is ability grouping really just tracking with a kinder name?
If we ability group in elementary are we setting students on their path for the rest of their academic career or are we indeed teaching them within their zone of proximal development and then spurring further growth? Are we able to group students in such a way that all are challenged at their level without breaking them apart? Can we effectively meet every single child’s needs within in a classroom setting during our instruction time without identifying which skill they specifically need to work on and them grouping them to work on them?
I would love your thoughts on this.
Pernille Ripp 
I think "ability grouping" is an even worse term, because "ability" has a much more permanent connotation. I don't ability group. However, I do create small groups based upon intervention for specific standards. The groups are fluid and the focus is small group instruction to help them master difficult concepts. Each concept group has students of different reading levels and language levels.
This year, my only real groups are for guided reading. Other groups are either student-designed or made by me with an eye more toward personalities than abilities. I have noticed that if personalities mesh, kids can put their heads together more than I have previously given them credit for. I thought a lot about my 5th graders when I had them, and how it was just so obvious what the groups indicated. Some groups finished pretty fast and others struggled. The distinction was clear. It makes for an inhospitable environment…
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I AGREE. I've said the same thing for years. Here's the argument against grouping given to me by my mother who was a teacher for 25 years. Students need modeling by their peers. If their peers are at the same level, where's the growth? Also, tests are not perfect. How do we know that we are teaching them at their level? Sometimes there are hidden talents which we do not nurture, because we have labeled the child. As we know, students often live up to our expectations. At my school, we have across grade level groupings for reading and English language development (K-5). A ridiculous amount of time is spent transitioning kids (and teacher time making groups). Also, groups are even less flexible because of the multiple teachers involved. To be honest, these are things imposed on us because of NCLB and state laws. Tragic.
Hi Donna, I actually do like my groups, they don't take much time to set up and they change often so I get to work with all the kids. I am more worried about the long-term groups and the power that lies in a name. Many of our groups are not strictly ability based but a good mix of abilities to promote peer to peer learning as well but I so agree with you that our expectations also set the course. I have high ones for my kids and they live up to them.Thank you for your comment,Pernille