This article reports of the effectiveness of introducing non-linear functions in a German Hauptschule. Some research based recommendations are provided for practitioners with the goal of improving student competencies in lieu of PISA.
"Non-linear functions in secondary school of lower qualification level (German Hauptschule),"
The Mathematics Enthusiast: Vol. 4
, Article 9.
Available at: http://scholarworks.umt.edu/tme/vol4/iss2/9