First we should understand the character of Kethu .
Kethu is a planet for Moksha ,
If a person gets wisdom he will have no attachment of material llife. In his point of view money,fame,political power,family life all are waste only.
If a person has kethu dhasa that person will gets all the characters of Kethu.That’s why people are considering kethu dhasa as worst.
But one thing if a person has kethu dhasa in school days it will affects his health or study sure.