SPS as a whole does not turn away kids. It will, and must, always assign a kid who lives in the school district to a school in the school district, and if that kid needs a particular sort of language learning assistance or special education assistance, it will (and must) provide it.
Adding another option will certainly change the dynamic of how students find schools, but I don't think you can model or predict how it will affect students getting to attend the school they most wanted. Within the district schools, that is differnt each year - did more parents want/need programs at Kennedy and a school with a swimming pool? A growing Union Square neighborhood school at Argenziano? A progressive program at Healey with mixed-age groups, looping, and a strong emphasis on creativity? A small old-fashioned brick school building with traditional education at Brown? A walking-distance school serving East Somerville? West Somerville? Winter Hill? etc? Some schools are consistently oversubscribed and hold a lottery, some vary every year. But any child who needs ELL education will be provided it, even if they don't get Unidos. And I will reiterate that I don't think that the language program in the charter proposal is anything like the bilingual program at Unidos.
It's not really adding another school to the "system" - it would be dding a separate admissions/lottery process open to residents of the same town, not adding an option (as in, rank your programs out of 7 choices - now you get 8 instead.) Many kids might, to take your example, apply to both UNIDOS and to SPCS, or to both Healey and to SPCS, and get a yes/no placement in SPCS, and then a school that might or might not have been their first choice in SPS, and then both the district and the charter school would have to reshuffle once the family's choice was made.
Also, in terms of adding options - I anticipate that will probably be a zero-sum addition unless a lot of additional funds appear out of the sky - one charter option appears, and one elementary option disappears, once the budget implications level out.
Re: Somerville schools aren't "true" public schools by your own definition.
Adding another option will certainly change the dynamic of how students find schools, but I don't think you can model or predict how it will affect students getting to attend the school they most wanted. Within the district schools, that is differnt each year - did more parents want/need programs at Kennedy and a school with a swimming pool? A growing Union Square neighborhood school at Argenziano? A progressive program at Healey with mixed-age groups, looping, and a strong emphasis on creativity? A small old-fashioned brick school building with traditional education at Brown? A walking-distance school serving East Somerville? West Somerville? Winter Hill? etc? Some schools are consistently oversubscribed and hold a lottery, some vary every year. But any child who needs ELL education will be provided it, even if they don't get Unidos. And I will reiterate that I don't think that the language program in the charter proposal is anything like the bilingual program at Unidos.
It's not really adding another school to the "system" - it would be dding a separate admissions/lottery process open to residents of the same town, not adding an option (as in, rank your programs out of 7 choices - now you get 8 instead.) Many kids might, to take your example, apply to both UNIDOS and to SPCS, or to both Healey and to SPCS, and get a yes/no placement in SPCS, and then a school that might or might not have been their first choice in SPS, and then both the district and the charter school would have to reshuffle once the family's choice was made.
Also, in terms of adding options - I anticipate that will probably be a zero-sum addition unless a lot of additional funds appear out of the sky - one charter option appears, and one elementary option disappears, once the budget implications level out.