This monograph examined the relationship between language proficiency (LP) and language and text analytical skills (LTAS) as frameworks for addressing comprehension difficulties resulting from terminology variation in life sciences textbooks. Fifteen (15) senior secondary science students, with varying degrees of language competences, were assigned to five (5) groups. A language proficiency test and a test that requires students to process variant life sciences terminology were administered to the two categories of students. A Chi-square test was used to determine whether there will be a significant difference in the performance of students on both tests. The result revealed a computed value of (X2 =18>3.84146) indicating a significant difference in the performance of the students on the language proficiency test and the language and text analytical skills test. Based on this finding, the study concluded that language proficiency-as narrowly defined by language educationists-is not always a factor of achievement in science. The study recommended that some linguistic explanations other than language proficiency are required in language-oriented discussions on achievement in science.