Two studies addressed key theoretical debates in theory of mind (ToM) development by comparing (a) deaf native signers (n = 18), (b) deaf late signers (n = 59), and (c) age-matched hearing persons (n = 74) in childhood (Study 1: n = 81) and adulthood (Study 2: n = 70) on tests of first- and second-order false belief and conversational sarcasm. Results showed ToM development to be a life span phenomenon for deaf and hearing people alike. Native and late signers were outperformed by hearing peers on advanced ToM in childhood (M = 9 years), but in adulthood (M = 40 years), native signers had caught up, whereas late signers had not. Findings highlight the extended importance of conversational interaction for ToM growth.