Found this on a Reddit forum Seems worthwhile reading. – “The Taliban just killed 130 people in a school, mostly children. Why is that somehow part of a rational strategy for them? How do they justify that to themselves?”
Answer:
The larger context right now is being ignored. Since June the Pakistani military has been conducting a military offensive in the Northwest Frontier Provinces. This area often called the FATA district is home to various Pakistani Taliban groups and tribal groups ( like the Mehsuds and Wazirs) with shifting allegiances. The Pakistani Taliban is influenced by

A) Deobandi Islamism which is a Southeast Asian variation of radical Islam: http://en.wikipedia.org/wiki/Deobandi

B) and its dominant influence is the Pashtun tribal ethos of Pashtunwali: http://en.wikipedia.org/wiki/Pashtunwali
These two influences have shaped Taliban religious and political ideology. Now, 80 % of the Taliban are Pashtuns, while Pakistan is divided into various ethnic and regional groups ( like Sindhs, Punjabis).

The Pashtuns are also in Afghanistan as the Durrand Line ( the border between Pakistan/Afghanistan) cuts between their ethnic ” homeland”. They don’t identify with the state of Pakistan.

Now, since the operation: http://en.wikipedia.org/wiki/Operation_Zarb-e-Azb was launched since the breakdown of the ceasefire with the Taliban and PM Nawaz Sharif’s gov’t and the Jinnah int’l airport attack in June, The Taliban consider the use of attacks on children and schools as a means of exacting revenge which is a major important thing in Pashtun culture. They see the deaths of their tribesmen as something that justifies these barbaric attacks. They have been scattered now into various cities in Pakistan as well, which makes it more dangerous.

The Pakistani Taliban are at war with the government in Islamabad. I would also like to add that the Taliban attacked an ARMY school, which means these kids were children of soldiers who were fighting in the NWFP. The tribes the Taliban protect there lost many children to the Pakistani military. This is cold blooded revenge for the Taliban at the same time sending a message to the Pakistani military to stay out of ” their” territory.

Edit: I am also going to add a Wiki link to the areas where the Pashtun people predominate. If you notice its in the area of the border region: http://en.wikipedia.org/wiki/Pashtun_people#mediaviewer/File:Pashtun_Language_Location_Map.svg

Edit 2: Wow.Thanks for the gold! I am only doing my duty as someone with a History degree. If you want some good sources I suggest two readings:
http://yalepress.yale.edu/book.asp?isbn=9780300178845
http://www.theguardian.com/books/2011/may/01/pakistan-hard-country-anatol-lieven-review

Edit 3: I wanted to clarify that my statements are not demeaning to Pashtun culture or to Pashtun people. I hope you don’t take offense. Most Pashtun are not Taliban. My point being was that most Taliban are Pashtun. I want to explain the socioeconomic and historical circumstances of a great people within the context of why the Taliban continue to exert influence.