1. Johnstone, R. (2010). Learning through English: Policies, Challenges and Prospects, British Council.
2. European Commission/EACEA/Eurydice (2017). Key Data on Teaching Languages at School in Europe—2017 Edition, Eurydice Report.
3. Huhta, A., and Leontjev, D. (2019). Kielenopetuksen Varhentamisen Kärkihankkeen Seurantapilotti, Final Report, University of Jyvaskyla, Centre for Applied Language Studies.
4. Inha, K. (2019, June 13). Vuosi Kärkihankentta Takana, Kieliverkoston Verkkolehden Teemanumero, [Online]. Available online: https://www.kieliverkosto.fi/fi/journals/kieli-koulutus-ja-yhteiskunta-kesakuu-2018/vuosi-karkihanketta-takana.
5. Moyer, A. (2004). Age, Accent and Experience in Second Language Acquisition: An Integrated Approach to Critical Period Inquiry, Multilingual Matters.