Speaking in a foreign language is considered challenging to both teach and learn. Virtual humans (VHs), as conversational agents (CAs), provide opportunities to practise speaking skills. Lower secondary school students (N = 25) engaged in an AI-based spoken dialogue system (SDS) and interacted verbally with VHs in simulated everyday-life scenarios to solve given tasks. Our analysis is based on system-generated metrics and self-reported experiences collected through questionnaires, logbooks, and interviews. Thematic analysis resulted in seven themes, revolving around the speaking practice method, scenarios and technology, which, in combination with descriptive statistics, enabled a deeper understanding of the students' experiences. The results indicate that, on average, they found it easy, fun, and safe, but sometimes frustrating in scenarios not always relevant to their everyday lives. Factors suggested as underlying the levels of experienced frustration include technical issues and constraints with the system, such as not being understood or heard as expected. The findings suggest that lower secondary school students conversing with VHs in the SDS in an institutional educational context facilitated a beneficial opportunity for practising speaking skills, especially pronunciation and interaction in dialogues, aligning with the key principles of second language acquisition (SLA) for language development.