This is a really loaded sentence for me. First of all, it connects to the earliest discussed ideas of "schools as a lousy place to learn" by Becker and issues of access (ex. butchers) by L&W. Second, institutional could mean the physical place, or the less physical but more important power/control relationships (probably both). Next, "inviting or prohibiting opportunities" points at he impact these institutions (not just individuals like teachers or master butchers) have on who gets to be a part of a community. Finally, this sentence in the midst of the author's description of situated events as a constellation is really reminding me of the multisited paper in that there is overlap between systems (or communities of practice) for a person and that often what happens in one is not only connected to the happenings in another, but might literally overflow into and impact the other.