Over the last decade, there has been an increased interest in investigation of assessment for learning. However, to date, there are still very few studies that investigated assessment for language learning or formative language assessment, focusing particularly on: (a) effects of formative assessment on learners’ linguistic development and on teachers’ teaching and lesson planning; (b) variables influencing the frequency and extent of effectiveness of formative assessment; (c) teachers’ and learners’ views on teacher feedback and learner peer- and self- assessment; and (d) fulfilment of the requirements set in the official United Kingdom (UK) policy documents on effective teaching and assessment of learners with English as an additional language (EAL), also known as English as an second language (ESL) in the United States (U.S.), in real classrooms. This article addressed these issues, and thus, extended the limited knowledge base on formative language assessment research to date. Moreover, through examining classroom-embedded language assessment processes from various perspectives, this research paper made a link between two research areas: (a) language testing and assessment; and (b) second language acquisition, also a relatively neglected field of research. This paper investigated two intact primary immersion classrooms, with learners as young as 8-10 years old and teachers whose teaching roles in the classrooms differed; two teachers were mainstream classroom teachers (CTs) and one was a mainstream teacher with specific responsibilities for language development in the school. The data were derived from literacy, numeracy, and science lessons through classroom observations and from the research participants through interviews. The data were firstly transcribed and coded qualitatively and then analysed both quantitatively and qualitatively. The findings revealed that various language assessment strategies were used regardless of the subject area of the lessons or role of the teachers and had formative potential for both the teachers and the learners. However, the frequency of use and extent of effectiveness of these strategies sometimes varied. It was also found that four out of five language assessment strategies, namely, teacher feedback, teacher questioning, learner peer-assessment, and learner self-assessment, had a clear positive effect on learners’ linguistic development, with the teachers and the learners overall reporting having a positive attitude to these strategies