A study published in the journal Economics of Education Review suggests that assigning pupils to the same teacher two years in a row may improve academic performance because teachers get to know their pupils and are able to adjust and target their teaching styles accordingly.
Andrew J Hill and Daniel B Jones used administrative data from North Carolina to observe the importance of pupil–teacher familiarity on academic performance in elementary (primary) school. They found that “looping”, in which an entire class moves to the next year with the same teacher, results in a small but statistically significant increase in pupil achievement. Pupils who spent a second year with the same teacher scored higher on end-of-year tests (on average 0.123 of a standard deviation) than those who weren’t matched. These benefits were greatest for minority pupils and lower-performing teachers (as measured by value-added).
Source: A teacher who knows me: The academic benefits of repeat student-teacher matches (June 2018) Economics of Education Review volume 64