Six hundred, 4-, 5-, and 6-year-old bilingual, rural, and urban children from southwestern, midwestern, eastern, and southern United States participated in a national study of Spanish/English bilingual development. Half of these children completed the English version of CIRCO (1980) sub-test 10-C, a productive language measure that requires children to relate a description of a two dimensional picture. Half of the children completed the Spanish version of this same instrument. Analyses were performed on these English and Spanish samples regarding Mean Length of Utterance and intrasentential language switching. Comparisons were possible across: age, rural/urban status, and region (and to some extent, Hispanic ethnicity). On measures of linguistic proficiency, consistent differences were observed in developmental trends for Spanish and English. For Spanish, linguistic proficiency measures increased from ages 4 to 5, then decreased at age 6. For English, these same measures showed a continuous increase across age groups. On language switching measures, regional differences were observed regardless of age. Almost no rural/urban differences were observed. These findings are discussed from both a language acquisition perspective and a bilingual education perspective. (Author/AH)