Every teacher in every school in the world faces daily challenges. These include a wide-range of issues from psychological learning disabilities such as dyslexia and dysgraphia, behavioral issues like ADHD, socio-economic status, medical issues such as autism and Fetal Alcohol Spectrum Disorder (FASD), lack of parental or administrative support, lack of resources (e.g. technology), and so on and and so on.
As educators, we should be thankful for these challenges. Yes, thankful. It is these challenges which make us even better facilitators of knowledge. Adaptation, reconfiguring our approaches, seeking long and short term solutions, and expanding our worldview are definitions of intelligent activity.
But, what is the most challenging educational environment? Obviously, there are many...too many and a high degree of variance in the population that ranges from the "Savage Inequalities" of Jonathan Kozol's urban schools, to the upscale private and privileged schools. In a land of disparity, why do we take broad, sweeping standards such as "Common Core" to be a serious attempt to produce educated young minds.
Either you repeat the same conventional doctrines everybody is saying, or else you say something true, and it will sound like it's from Neptune.