A I'd recommend a running record as a way of keeping track. They were developed by Marie Clay, who created the reading recovery programme. A running record is the only method I know which analyses the process as the child actually reads. Basically, as the child reads (usually a book that is known to some degree - it can be geared to the level the child is at) you mark up a copy of the text, noting the child's errors. You are then able to analyse what kinds of information the child draws on and the strategies they use. Used once or twice a term, depending on resources, this gives a teacher the opportunity to focus on areas for teaching. Miscue analysis is a similar approach but is used with older children, with an unknown text.
The procedure is simple to learn and informative. Working with teachers, I have seen how running record and miscue analysis develop professional knowledge and confidence, making teachers more skilled observers of children's reading. I also find that keeping simple notes for reading one-to-one with a child, using the headings "book title", "date", "child's strategies", and "teaching strategies", in a loose leaf folder can be a helpful cumulative record, shared between teacher, teaching assistant, and reading volunteer.