This is the section of Scholastic's website introducing the Scholastic Reading Inventory (SRI) software. I've worked extensively with this software in the past, and it can do some pretty great stuff.
With the software, you can simultaneously measure the lexile score of as many different students as you have computers. The test takes between 20 and 40 minutes, depending on various factors, and the questions on the assessment are tailored to the interests of the student at the outset of the test. While the ideal setting is testing 10-12 students at a time, as thias size group makes monitoring their engagement and effort a little easier, I've tested groups as large as 25 kids split in 2 different rooms all at once. Pretty amazing.
The system can be based off an on-site server, or hosted remotely through the internet. It does cost money, but the cost is not prohibitive.
The system can also do things such as track the progress of an individual student throughout the year, as well as track entire classes, or the progress of specified groups (nod to NCLB).
After each student completes the assessment, they are able to log into a database that can recommend appropriately leveled texts according to their interests. Overall, just a really great resource if your school has the cash to invest.