Does Acts 15:21 assume new believers would learn and follow the law from synagogues on sabbath? Acts 15:19-21 (NIV, Emph mine)


  19 “It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God. 20 Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood. 21 For the law of Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath.” 


This verse is used for and against observing law. Seems like this could mean either, "There are enough people following Moses and observing the law, so no need for more people to follow the law." or "The law is repeated in synagogues and new believers will go to synagogues, so they'll learn and follow them later."
I don't think this is saying the Gentiles should have to learn the law of Moses.  Quite the contrary, I believe it is saying they should not have to be burdened with the law of Moses.

Earlier in Acts 15 Peter asks why should the Gentiles be required to follow the law the Jews have.


  Acts 15:10-11 NIV
  10 Now then, why do you try to test God by putting on the necks of
  Gentiles a yoke that neither we nor our ancestors have been able to
  bear? 11 No! We believe it is through the grace of our Lord Jesus that
  we are saved, just as they are.


When contrasted with this, I would understand James response in verses 19-21 to be saying most of the law of Moses would be an extreme burden on the Gentiles, considering even the Jews who heard the law weekly were not able to uphold it.