Rochovska, I., Huľová, Z., Klein, V., & Gašparová, M. (2019). THE OPINIONS OF PRE-PRIMARY EDUCATION TEACHERS ON THE ADVANTAGES AND DISADVANTAGES OF HETEROGENEOUS AGE GROUPS. Problems of Education in the 21st Century, Problems of Education in the 21st Century, 77(3), Continuous. presented at the June/2019. doi:https://doi.org/10.33225/pec/19.77.424