Recent studies on technology-mediated task-based learning have shown the impact of task design and modality on English as a foreign language (EFL) learning. However, it is unclear what effect technology-mediated tasks have on learners’ English language skills. This paper presents a classroom-based study that showed how using technology-mediated tasks impacted students’ learning experiences and fostered the development of specific speaking and writing subskills in an EFL secondary education context. Forty-two EFL intermediate learners completed two speaking and two writing tasks from the Cambridge B2 First exam using mobile devices. The participants were divided into a pen-and-paper group (N = 21) and an iPad group (N = 21). Learning outcomes were measured using a pre-test/post-test design with a statistical comparison of ratings across tasks. A qualitative content analysis of lesson observations and student and teacher interviews served as an additional dataset to shed light on learners’ experiences. Descriptive statistics revealed that the iPad group achieved higher scores in pronunciation and accuracy (speaking) and essay organisation features (writing). Tasks involving the active use of the tool for content creation, rehearsing speaking performances, and accessing authentic materials were the most successful among students.