I see some schools operating under the UK-system have entry requirements listed like "must have completed 10+2+3, 11+1+3, or 11+2+2". What do these mean? If I've completed high school and a BA in the US, is that likely equivalent to any of these?
I think it's like this (copied): If the national education pattern is 10+2+3, with first 10 years devoted to general education, 2 years for diversification from general education to specialised academic or vocational courses and 3 years for degree programmes. In other words, first 12 years of education is called school education, which does not include pre-primary education comprising of nursery and kindergarten stages. At the +2 stage, a student is in a position to exercise a choice to select a stream (academic or vocational), keeping in view his interests and professional pursuit. So, if I've gotten it right, someone who goes through a 10+2+3 pattern winds up with a Bachelors degree (without the fourth year Honors degree). I think that, based on this, you can extrapolate the other systems.
The first number is years of primary and secondary school. The last two numbers relate to additional qualifications such as GCSE and GCE A Levels. Qualifications: what the different levels mean : Directgov - Education and learning