Is speaking a minority language (e,g, Spanish) at home is better or worse?

King and Mackey mention a very interesting study which found that it’s almost better to speak the minority language at home
After comparing two groups (group 1: mixed families speaking Engish at home , group 2: mixed families speaking Spanish at home) “Dolson (1985) found that the two groups performed similarly in terms of (1) English reading skills, (2) oral reading skills, (3) length of time classified as Limited English Proficient by the school, (4) attendance rates, and (5) disciplinary referrals. He found that the children from Spanishspeaking homes performed significantly better on measures of (1) mathematics skills, (2) Spanish reading vocabulary, (3) academic grade point average, (4) effort grade point average, and (5) retention. This work strongly suggests that there are important advantages (and no apparent disadvantages) to continuing to use Spanish at home.” (p. 114)
Source: King, K., & Mackey, A. (2007). The bilingual edge: Why, when, and how to teach your child a second language. New York: Collins