I guess, your DD will have to be at a "reasonable" level in English for you to get a decent guess. My DD6's leap verbally was pretty significant (jumped from 92% to 99.8th percentile).
I have heard that kids need to have at least 2-3 years of regular, full day school to catch up. We tested my DD, for the second time, after 1 year of K and 3 days of 1st grade; so this second time around is probably still, technically, an underestimate (although in practical matters it doesn't really matter).
.
DD is only 27mo and as I work full time has been in english daycare environment for 2 years now. She speaks both languages quite well for her age although in our home language she can express her toughs more "sophisticated". She learns our language from adults and english from toddlers. She obviously can not learn to speak any better english than her peers. In her english I hear her using identical sentences with her friends. We do read in both languages but whenever there is something in a book she wants me to explain I tend to change to our own language. I really don't see her being able to show her full potential in english at 3 (after 3 years fullday english daycare), she could just show the potential of her friends whom she learned to speak from.
