Hi Sarah,
Makaton, even full blown, is only a couple of hundred signs used to support spoken English.
Many settings use Makaton as part of their daily work, and children usually benefit from the addition of gesture rather than suffer.
I am surprised that it was causing confusion since usually when using signed communication the hands and face are in frame. In BSL many signs are distinguished by the facial expression.
I was involved in a project to deliver science in BSL and English to a yr 2 class in conjunction with a deaf group. The children gained more secure science concepts than the classes not involved. This was not written up as full research because I never had the time. Similarly in the days when schools could choose how to teach phonics, Jolly Phonics was often used in largely EAL schools because it added gesture and kinaesthetic learning to the mix. The Jolly Phonics site had some research on this.
The TA may have been unable to help themselves, I move between signed and non signed environments mid week, and find myself adding BSL to my teaching by accident.
Makaton is not a language, it is not sign language, it does not provide enough linguistic structures, vocabulary and concept development to be useful for the deaf population.
It is, however, helpful for students who will struggle to develop language. It is also, in my experience, not unhelpful with younger children, and can enable younger EAL learners to understand class routines, when used as part of whole class practice.
I cannot see singling out one child to use it as at all helpful, as it clearly will not support peer interaction which is essential. So I would say get the teacher to build into whole class practice, especially round routines, stop teaching it to one child, add in some Russian, and provide comprehensible input and meaningful interaction in spoken English instead.