Classrooms with higher teaching quality were associated with higher learning outcomes in mathematics and science. Classrooms where teachers reported high degrees of limitations to teaching in the classroom--including disruptive students or students with language barriers--were associated with lower learning outcomes. These are two of the important findings of the Northern Lights book project examining the current state and trends in mathematics and science performance in Nordic primary schools using TIMSS (Trends in International Mathematics and Science Study) data from 2011, 2015, and 2019. The study also identified a worrying trend: a decline in aspects of teaching quality and increased limitations to teaching between 2011 and 2019. These negative changes were associated with decreased achievement over time. Fewer students perceived the teaching as supportive and clear, while teachers increasingly reported challenges in their teaching and learning, including students' lack of prior knowledge and absenteeism.