Issues with Common Core and Eureka Math

No textbook to show how to accomplish the problems. Same problems in the classwork portion do not always translate on how to do the homework.
Adults in our age learned a different way to do these problems. If I do not understand the principles of Eureka Math and the Common Core how can I help my child with their homework. (Ex. Order of operations – not allowed to use parenthesis)
Unable to stay after class for additional help, but can only come during zero hour. This conflicts with another class during zero hour that he is being graded upon and counts as a credit.
Says he’s turned in homework, but she does not have copies of these.

How can we help our children if we do not know how to do them. We do not have the Eureka Math answer key. Can we get access to the online curriculum some how so we can see examples with answers to help walk them through how to do a problem. Much of our disagreements come because I explain how to do a problem, but he tells me it’s not the way his teacher taught him. I then ask how she taught you and he is unable to explain.
What additional practice can he do this week and weekend that will help on the assessment.
Tutor options that understand this process.
Where do we go from here to help him recover from this awful semester and set him up for success during next two marking periods.