Lizzie is looking forward to the science class field trip, but she is mortified when she finds out that her mother is a last-minute replacement as the girls' chaperone. Lizzie fears that her mother will embarrass her to death, and Mom does a pretty good job of doing just that while they are competing with the boys on a nature walk. But Mrs. McGuire proves how cool she can be when she helps the girls get back at the boys for a prank they pulled then takes all the blame herself. Back at home, Matt and Mr. McGuire are left on their own and try to cook for themselves.

When a babysitter cancels on the McGuires, Lizzie suggests that she's old enough to do the job for her brother Matt, but mom and dad say no. After much persuasion from Lizzie they relent, and Miranda and Gordo also come over to help. After Mr. and Mrs. McGuire leave, Matt generally causes havoc, spilling grape juice on the rug, acting bratty and taking advantage of Lizzie, who badly wants to impress her parents with her responsibility. Miranda and Gordo aren't much help as they won't follow Lizzie's orders either. At the restaurant Sam McGuire wants to sneak home and check on his daughter and son; Jo doesn't like the idea, but says just don't let them see you. Meanwhile at the house, Matt has knocked out the power. Mr. McGuire tries to peer in the window and goes tumbling over. The kids think he's a burglar and call the police. Mr. McGuire tries to get in the locked house and the kids wage a battle against him reminiscent of the movie Home Alone. The police come to arrest Sam. After al

Lizzie and Miranda note that when a girl gets her first bra, her personality somehow seems to change. They decide they are ready for their first, and hatch a plan to get Lizzie's mom to take them to the mall where they will shop for ""school supplies."" Lizzie is a terrible liar, though, and blurts out the real reason for the trip. Mom is overjoyed to help the girls out, but she embarrasses them as they are shopping. Lizzie is very harsh with her mother, telling her that she and Miranda are old enough to do their own shopping and to leave them alone. The girls face further embarrassment when they run into Kate, Claire, and their English teacher Mr. Coppersmith. They also find that they don't know what to look for.

Matt is irritating Lizzie with his magic tricks while she's trying to do homework. Soon they are fighting like cats and dogs--or brother and sister--much to the annoyance of their parents. But as soon as Sam and Jo stop them, they go right back to fighting.

At school Ethan Craft speaks to Lizzie and Miranda, but Lizzie is so tongue-tied she can barely utter a word. Mr. Escobar announces a charity drive and asks for volunteers. Lizzie thinks she'll be too busy until she hears that Ethan will be there. At home Lizzie is making some cookies for the event when Matt tries out another trick. This time he handcuffs himself to his sister, but he can't get the cuffs loose. Mom spies the key and hides it, thinking that if the kids are forced to spend a few hours chained together, they might learn to get along better. Now Lizzie is facing the horror of going to the charity drive with her little brother stuck on her arm!

Gordo wants to raise money for a new stereo, so Miranda and Lizzie suggest he tutor students who need help in math. His first student is Ethan Craft, much to the girls' delight. When Gordo is working with Ethan at the Digital Bean, Lizzie and Miranda keep trying to horn in on the action and end up spilling drinks all over the guys' papers. Gordo gets mad at them and suggests that they aren't smart enough to help him tutor anyway. The girls get angry right back at him and leave. Meanwhile, Matt and his friend Oscar are looking for something exciting to do. They decide to become ""super heroes"" Matt Man and the Incredible Oscar. They go around the neighborhood in costume trying to do good deeds, but all they do is annoy the neighbors.

Hoping to win a trip to Miami, Lizzie, Miranda and Gordo team up to enter the school's ""Fact-athlon."" Their rival team consists of Kate Sanders, Larry Tudgeman and Claire Miller. But things start to look a little bleak when the faculty advisor Lizzie and company chose is replaced by substitute teacher Mr. Dig. But to their surprise, Mr. Dig manages to turn studying into something fun and interesting with his unusual approaches. By the time the competition starts, Lizzie's team is confident while Kate, Larry and Claire are feeling the pressure. But Kate's team beats Lizzie's team badly when there are too many questions about dates and names rather than ""how and why"" problems. Kate and her teammates gloat over their win and Mr. Dig is ready to leave his job at the school because he thinks he let the team down, But Lizzie, Gordo and Miranda convince him they they actually did learn a lot and that they had a good time doing it.

Lizzie learns what sort of things Ethan Craft is into in order to transform herself into his ideal date.

Lizzie and Gordo worry about Miranda's diet; Matt expresses interest in the fine arts.

Gordo skips a grade and gets promoted to high school. After initial euphoria, Lizzie and Miranda start to miss Gordo.

Lizzie starts a column on her school's website, but soon finds it difficult to handle when her good intentions backfire.

Miranda is throwing a big house party, and refuses to invite Larry. Lizzie feels bad about it and decides to give him a makeover and sneak him into the party.