Social mobility: social mobility refers to our chances of moving up or down within the american class structure. what do you think is the most important factor that leads to upward mobility? and why do you feel that way? race or ethnicity gender social class at birth hard work and education

Although all of the options are important factors to determine social movility, I beleive that one amongst them has more impact. Social class at birth makes a significant difference. It is like a stating point in life, some people start with some advantages (like being born in a wealthy and educated family) and other with disadvantages (being born in a poor family with no access to education).  

Although race or ethnicity and gender are important too, they can have a stronger or weaker impact depending of your social class. A person that forms part of a minority, for example, african american, will have a very different life depending on the economic situation of the family.

It is true that hard work and education is also needed but, again, social class can lead you to a more familiar and direct contact with them.

there is an explationation of this on a site called crash   course world history 1