The English verb "be" has always been a perceived problem for Chinese ESL learners, however, few studies have been conducted with a specific focus on the interlanguage "be" of Chinese ESL learners. This paper examines the variable use of the English verb "be" of 270 Hong Kong primary school children for developmental patterns of English language acquisition versus L1 transfer phenomena. Although there are traces of transfer, the results do not suggest a strong role for L1 transfer in the use of English "be" but tend towards developmental aspects of omission and overgeneralisation, nonetheless a basic indication of L2 systematicity with accountable variations. A subsequent examination into the children's school textbooks reveal other significant affective variables such as input and classroom conditions for learning, which appear to interact with other learning factors to increase the variability of Chinese learners' interlanguage "be." (Contains 2 notes and 3 tables.)