allah the almighty said:
1- (indeed, allah orders justice and good conduct and giving to relatives and forbids immorality and bad conduct and oppression. he admonishes you that perhaps you will be reminded) (an-nahl:90).
2- (and i have been commanded to do justice among you) (as-shura: 15).
3- (do not let the hatred of a people prevent you from being just. be just; that is nearer to righteousness. and fear allah; indeed, allah is acquainted with what you do) (al-ma'eda: 8).
4- (and when you testify, be just, even if [it concerns] a near relative. and the covenant of allah fulfill. this has he instructed you that you may remember) (al-an'am: 152).
5- (o you who have believed, be persistently standing firm in justice, witnesses for allah, even if it be against yourselves or parents and relatives. whether one is rich or poor, allah is more worthy of both. so follow not [personal] inclination, lest you not be just. and if you distort [your testimony] or refuse [to give it], then indeed allah is ever, with what you do, acquainted) (al-nisa': 135) …
in the first verse, allah the almighty ordered his servants to be just and deal with people justly. each ruler should deal justly with his people and should perform his duty toward them. this includes the deputy rulers, judges, deputy judges and the persons who assume any kind of authority. they all should deal justly with people. the teacher also has a kind of authority on his students and should deal justly with them.
in the second verse, allah the almighty ordered his prophet, peace be upon him, to deal justly with the people of the scripture (jews & christians) and not to let enmity prevent dealing justly with them.
in the third verse, allah the almighty ordered people to be just in dealing with each other and not to let hatred prevent them from dealing justly with the enemies. the verse demonstrated also that doing justice, even with the enemies, will make us nearer to righteousness.
in the fourth and fifth verses, allah the almighty ordered the believers to be just in their statements and deeds toward their relatives and other people alike, without bias, and not to follow their inclinations. these verses demonstrated the importance of dealing justly with people and treating them equally.
the prophet, peace be upon him, set several supreme examples for dealing justly with people and treating them equally.
1- aisha, may allah be pleased with her, reported: the quraish people became very worried about the makhzumiya lady who had committed theft (as her hand will be cut off as a punishment for stealing). they said, "nobody can speak (in favor of the lady) to the prophet, peace be upon him, and nobody dares do that except usama who is the closet man to prophet, peace be upon him. "when usama spoke to the prophet about that matter, the prophet, peace be upon him, said: ((do you intercede (with me) to violate one of the legal punishments legislated by allah?)) then he got up and addressed the people, saying: ((o people! the nations before you went astray because if a noble person committed theft, they used to excuse him, but if a weak person among them committed theft, they used to inflict the legal punishment on him. by allah, if fatima, the daughter of muhammad committed theft, muhammad will cut off her hand!)) al-bukhari (3288), muslim (1688).
2- nu'man bin basheer reported: my father donated to me some of his property. my mother, amra bint rawaha said: i shall not be pleased (with this act) until you make the prophet - peace be upon him- a witness to it. my father went to the prophet, peace be upon him, in order to make him the witness of the donation given to me. the prophet, peace be upon him, said to him: (have you done the same with every son of yours?) he said: no. thereupon he (the prophet) said: (fear allah, and observe equity in case of your children). my father returned and got back the gift. in another narration for the same hadith, the prophet, peace be upon him replied: (then don't call me to be a witness, for i cannot be witness to an injustice). muslim (1623)
teachers have a kind of authority over their students in terms of assigning them with homework, making tests, determining their scores and other powers; therefore, teachers should deal justly with their students and should treat them equally, without any bias toward relatives or friends.
if the teacher practiced any kind of discrimination toward his students, this action will cause confusion, tension and hostility between the students and will widen the gap between the teacher and his students; therefore, the teacher should be keen to deal justly and equally with all of his students in order to ensure spreading love, respect and brotherhood among them.