The scene where Nellie and Willie taunt Laura outside the mercantile is interesting. They spot Laura walking with Miss Beadle and smile wickedly. I'm not sure what they thought they were going to do with Miss Beadle present. Nellie and Willie are typically on their best behavior in front of adults, especially their teacher. Unfortunately, Laura helped them by choosing to stay outdoors. Perhaps she didn't want them to see Miss Beadle buying her the tablets (but I'm sure her teacher would have been discreet and absolutely would not have made it evident that the tablets were for Laura). By staying outside, where no one could see or hear, Laura gave Nellie and Willie the exact opportunity they were looking for.
Reply: Being such naturally deviant children, I don't think Nellie and Willie were looking to scrutinize Laura right in front of Miss Beadle. It seems that the two of them were mostly trying to stare Laura down and make her feel like less than them. Also, considering that Laura knew what they were like, and because she was so young and probably didn't think of the alternative, she decided it was better to avoid walking inside with Miss Beadle and making it obvious that her teacher was buying school supplies for her. After all, Nellie and Willie would have undoubtedly followed Laura inside if she had done so, and they would have nailed her later--so really, either way, Laura didn't have much of a chance in avoiding the teasing.