State law requires districts to identify and serve highly capable students, and afaik all local districts have some kind of program. However, the entrance matrices, program expectations, and even what the programs provide can be quite different.
In addition to the 3 school districts Laurie listed, be sure to look into Northshore -- it's north of LWSD but the border is not always where you'd expect to be.
If you are moving now or mid-year, be sure to ask districts what they do about people moving in after their regular testing dates.
Also I would not look at test scores alone, especially if your child is 2E or is EG/PG. We left an exceptionally high-bar program in one district because the district was incapable of providing adequate special ed services, and moved to a much less exclusive program where the administration was flexible and welcoming. Our current program is NOT as strenuous and our school is lower-scoring in general, BUT the district has been easy to work with for things like allowing DD to do AoPS math during her regular math time in elementary school. Our previous school's high-scoring program would have allowed her to go up exactly one grade level in math.
