Some researchers have posited a &;ldquo;natural&;rdquo; order of acquisition of English grammatical morphemes common to all learners of English as a second language, but no single cause has been shown for this phenomenon. This meta-analysis investigated whether a combination of five determinants (perceptual salience, semantic complexity, morphophonological regularity, syntactic category, and frequency) accounts for a large part of the total variance found in acquisition order. Oral production data from 12 studies over almost 25 years, together involving 924 subjects, were pooled. Multiple regression analysis showed that a very large portion of the total variance in acquisition order is explained by the combination of the five determinants. We suggest research on other potential contributing factors and discuss the need for similar research in other languages.