The first TWI program in the United States began in 1963. For the next 20 years, the growth of TWI programs was minimal, with fewer than 10 documented programs in operation before 1981. The majority of programs in existence today were established during the past two decades. The 2000 Directory includes 248 TWI programs in 23 states and the District of Columbia. There has also been considerable expansion within existing programs: Many have reported adding new grade levels each year, and 40 programs now extend into middle or high school.

Program location. The majority of TWI programs are in public schools; only four are operated by private schools. Nearly a quarter of the public school programs operate in specialized environments: 11 are housed in charter schools and 53 in magnet schools. California has the most programs operating in specialized environments, with eight charter school programs and 22 magnet school programs. Relatively few TWI programs (32) are whole-school programs. About three quarters of the elementary programs (191) operate as strands within schools, as do all of the secondary programs (32). Twenty-five programs did not respond to this question.

Languages of instruction. Most TWI programs are Spanish/English (234). The other programs are Chinese/English (5), French/English (5), Korean/English (3), and Navajo/English (2). (One school houses both a Spanish/English and a Chinese/English program.) The majority of students enrolled in these programs are native speakers of one or both languages of instruction. In 37 programs, however, more than 1% of the students are native speakers of a language not used in the program (i.e., third language speakers). In nine programs, 5% are third language speakers.