The ambiguity of words and signs as a resource or obstacle in group discussions is studied.How deaf and hearing students aged 13–15 years elaborate on ecological concepts throughdialogue is described. Group interviews were conducted with 14 hearing and 18 deafstudents. Probes were used to initiate discussion about the different meanings ofecological concepts: producer, consumer, nutrients/nutriment, food-chain and cycles. Theresults show that the dialogues are less elaborated for deaf learners than for hearinglearners. It is argued that dialogues between hearing students have a greater chance ofbecoming ‘joint productive activity’, since words in Swedish pave the way for sharedmeaning-making. To deaf learners, differences in connotation between the Swedish wordsand the signs used lead to uncertainty and unproductive lines of reasoning. Oneimplication for instruction is that this bilingual communication needs to be taken intoconsideration to a much greater extent.