I am test-driving a new piano teacher during the summer vacation. After a diagnostic session, I have been assigned a number of Brahms exercises (8a, 8b, 9a, 26a, etc) to work on moving my hands into different positions, improve evenness/accuracy, reduce locking up & return to rest/claw position, better stretch, etc.

I have found that working on some of these, particularly 26a, is increasing tension rather than reducing. The first week was actually painful. This teacher then indicated that I need to do them very sloooowly and initially only under his supervision to avoid injury. Sounds kind of dangerous.

Anyone have experience with Brahms exercises? Any advice for me on proceeding?

I went through the Brahms exercises and found them very helpful. Your teacher's advice makes sense -- do them very slowly. Presumably, when you do them under his supervision, he will be able to observe the sources of tension and be able to help you with that.
I think the first step in reducing tension is to become
consiously aware of it -- then you need to pay attention to it whenever you play and make a conscious effort to relax whatever is tense (fingers, hand, wrist, arm, shoulder, back, etc.) A good teacher can be very helpful with this -- if he is paying attention and being observant, he will be able to help you recognize when you are tense.

Helene, Thanks for this. Had a good discussion with this teacher; spent a whole lesson just slowly feeling the keyboard and experiencing where and how to build in rest & relax spots both in the exercises and in some music.

Have spent the last days working on 8ab and 26a following your advice, particularly "...reducing tension is to become consciously aware of it -- then you need to pay attention to it when you play and make a conscious effort to relax whatever is tense."

Starting to see the value from these exercises, and: no pain.

Good. My general belief is that if you experience pain when playing then you are doing something wrong -- and unnecessary tension is often involved. I worked though the entire book of these Brahms exercises and never had any pain. There are some that I still play every day, including the one that involves stretching out to the tenth (is that number 26?). I think my arpeggios have become more accurate from doing that exercise. However, I have to learn everything by starting at an excruciatingly slow speed to train my fingers to get to the right notes. Play them slowly enough so that you can think about keeping hands, arms, fingers, back, etc relaxed. Try to maintain this relaxation as you build up speed. My own tension problems tend to be in the shoulders and back, rather than in hands and arms, and I am typically unaware of the tension until someone (like my teacher) points it out.