Ullrich, Dieter; Ullrich, Katja; Marten, Magret (September 2014). "A longitudinal assessment of early childhood education with integrated speech therapy for children with significant language impairment in Germany: Longitudinal assessment of early childhood education with integrated speech therapy". International Journal of Language & Communication Disorders. 49 (5): 558–566. doi:10.1111/1460-6984.12092. PMID24939594.
Ullrich, Dieter; Ullrich, Katja; Marten, Magret (September 2014). "A longitudinal assessment of early childhood education with integrated speech therapy for children with significant language impairment in Germany: Longitudinal assessment of early childhood education with integrated speech therapy". International Journal of Language & Communication Disorders. 49 (5): 558–566. doi:10.1111/1460-6984.12092. PMID24939594.