“A מחנך must realize that not only is it essential for him to use appropriate phrases in lessons, but that their manner of expression – whether he expresses them politely and patiently, or irritably and derisively – also affects the foundation of education and guidance. 

The benefits of true חינוך and הדרכה - guidance are attainable only through the observance and meticulous fulfillment of all the related prerequisites. Only then will the חינוך and guidance endure forever, and manifold ברכות will be bestowed upon the מחנך”

(Source: כללי החינוך והדרכה פרק ה )