You only need your highest degree evaluated. ECA is required for two purposes only (http://www.cic.gc.ca/english/immigrate/skilled/assessment.asp):Read all the comments。。。still dont know the conclusion...
a) FSWP eligibility
b) CRS points
In a) you need an ECA for your highest degree in order to get the highest possible score (over 100 points).
in b) you also need only the highest degree assessed as stated by CIC here: http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=991&top=29
"To get the most points possible for your education under the Comprehensive Ranking System, you should get your highest degree, diploma or certificate assessed (PhD, MA, BA)"
The only exception is where the combination of two degrees gives you more points than the highest degree and you want to claim this higher score. But as CIC states: "You must submit an ECA for all levels of completed foreign education you want us to consider. It is up to you to decide which credentials to have assessed".
Also read here (Q6): http://www.canadavisa.com/canada-immigration-discussion-board/threads/all-you-need-to-know-about-getting-your-educational-credentials-assessed.408311/