Sparta's ruthless education may have been controversial, but it made them into one of the most battle-hardened city-states to ever walk the earth. The Spartans' notoriously tough education allowed them to become one of the largest military powers of their time, even though their population was relatively small. Although Spartan education was brutal by modern standards, the system was extremely beneficial to the country and its survival. The strengths of Spartan education did outweigh the weaknesses for three reasons: it provided physical training, training of mentality, and important life skills.
The brutality of Spartan education forced young Spartan boys to become tougher, and didn't leave room any slack. The most obvious example of this is the harsh conditions young Spartan boys were forced to put up with. These conditions forced members of the agoge to either adapt and harden themselves, or die. In addition, Spartan boys were not provided with much, and had to live through the year with only 1 garment and scarce amounts of food. Finally, girls were not exempt from physical training, because Spartans believed that strong parents produced strong offspring. All of these aspects of Spartan education kept young children extremely fit and in shape, and also helped them adapt to tough conditions. These skills would be incredibly valuable once they moved on to become adults.
Although the Spartans were mainly focused on physical dominance, they were also taught to have a tough mentality. The scarce amount of resources provided to young Spartans prevented them from becoming spoiled, which would prepare them better for adult life. Discipline and obedience were also important concepts taught at the agoge. Finally, young Spartan boys were taught to show respect to those who deserved it; namely, men who were older than them. Oftentimes, people are easily hurt or influenced by words and peer pressure among many other forms of non-physical forms of influence, but the Spartans were trained to withstand the effect of these kinds of situations.
Finally, Spartan education taught young Spartans many important life skills. As mentioned earlier, Spartans were almost always being trained to survive under harsh conditions, which made them more resilient and able to withstand pain in the future. Also, because they were only allowed one garment throughout the whole year, they were taught to easily adapt to any type of weather. They were also taught to read and write, but, because this was purely for practical reasons, they were effectively prevented from wasting time reading and writing non-essential text, which gave them more time to focus on more important tasks at hand. These aspects of Spartan education kept Spartans both effective and resilient, and provided great boons to their lives in the future.
It is true that Spartan education had some weaknesses when it came to the harshness it exhibited on young children. However, the three reasons presented above - that Spartan education provided both physical and mental training, in addition to important life skills - show that, in the end, the strengths of Spartan education outweighed its weaknesses.